Funds are requested under the Biomedical Research Support Shared Instrumentation Program for the acquisition of a computer-based interactive graphics facility for macromolecular modelling. The particular system requested consists of a Vector General 3404 color graphics system and a VAX 11/750 host computer. The major users on this application are investigating a number of fundamental problems in structural biology, including the structural basis of bioenergetics of gene regulation and sequence-specific DNA recognition, of enzyme-substrate interactions, of hemoglobin function and pathology, of cytoskeletal assembly, and of DNA packaging in eukaryotic cells. Each of these projects now has (or will by the time this grant could be funded have) an immediate, major need for the graphics system that we are requesting. Currently there is no graphics facility available for our use in the Baltimore-Washington area, and we feel that such a graphics facility is a fundamental tool of modern structural biology. It is anticipated that about 50% of the use of the instrument will be for fitting molecular models to electron density maps; 20% will be devoted to the modelling of protein-DNA interactions; 20% to NMR-based conformational searches and enzyme-substrate docking studies; and 10% to the study of complex structures such as HbS fibers and actin. The particular system that we request should provide an economical and workable facility that will meet the needs of the major users and of the overall reseach community at the Johns Hopkins Medical School.